1. Field of the Invention
The present invention relates generally to the field of disk drives, and more particularly, to a disk drive of a perpendicular magnetic recording system that uses a double-layered disk medium for suppressing adverse effects caused by magnetic disturbances.
2. Description of the Related Art
In recent years, in the field of magnetic disk drives, attention has been paid to a perpendicular magnetic recording system, in which a magnetized area, corresponding to recorded data, is formed in a perpendicular (thickness) direction of the disk medium (hereinafter, simply referred to as “a disk”).
For the disk drive of a perpendicular magnetic recording system, use is normally made of a double-layered disk having a magnetic recording layer capable of perpendicular magnetic recording, and a soft magnetic layer provided between the magnetic recording layer and a substrate.
Further, the disk drive uses a magnetic head provided, on a slider of a head body, with separate read and write heads. The write head element is comprised of, for example, a single pole type head element suitable for a perpendicular magnetic recording system. The read head element is comprised of, for example, a spin-valve MR (magnetoresistive) element or a GMR (giant MR) element such as a TMR (tunneling MR) element. The GMR element is comprised of a magnetoresistive-type magnetism-detection element.
In the disk drive of a perpendicular magnetic recording system, the recording magnetic flux applied from the write head element to the disk is also received by the soft magnetic layer to allow effective magnetic recording.
Here, in a perpendicular magnetic recording type disk drive, the soft magnetic layer is used to improve the magnetic recording efficiency also highly sensitive to magnetic disturbances, which is a problem. Magnetic disturbances are external magnetic fields generated, from a spindle motor (SPM) in the drive, and a voice coil motor (VCM) of an actuator. The SPM is a motor configured to rotate the disk. The actuator has a mounted magnetic head (slider) and is comprised of a mechanism configured to move a read/write head to a target position on the disk.
Such magnetic disturbance makes the recording magnetization of the disk unstable and also exerts an adverse effect on the GMR element of the read head. It has been confirmed that, if, in particular, a magnetic field from the magnetic disturbance is emphasized by the soft magnetic layer and applied to the read head element (GMR element), then a read signal waveform which is outputted from the read head element suffers a distortion, etc., to cause the read error rate to be deteriorated.
As the prior art technique, a technique has been proposed for suppressing any adverse effect from an external magnetic field applied in a longitudinal direction of the disk (See, the example, JP PAT APPLN KOKAI PUBLICATION NO. 2000-90424).
In this prior art, the permeability of the soft magnetic layer is made relatively small and, by doing so, the reactivity of the magnetization of the soft magnetic layer under the external magnetic field is reduced, to suppress the magnetic flux of the magnetic disturbance from being concentrated onto the magnetic head.
In the prior art technique, it is possible to suppress any adverse effect from the external magnetic field applied in the longitudinal direction of the disk, but it is not necessarily effective for a magnetic field of a magnetic disturbance applied in a direction perpendicular to the disk.